1. Field of the Invention
The invention relates to a current mirror for generating a substantially identical current flow in two parallel current paths. In particular, the invention relates to a current mirror having two transistors, in which it is desirable to keep the voltage across the active terminals of each respective transistor substantially the same as the voltage dropped across the active terminals of the other of the transistors.
2. Description of the Related Art
Transistors are charge-controlled devices that generally have three terminals: two active terminals and a control terminal. Conduction between the two active terminals depends on the availability of charge carriers, which is typically controlled by a voltage applied to the control terminal. There are two principal varieties of transistor: field-effect transistors (FETs) and bipolar junction transistors (BJTs). The operation of each type of transistor is slightly different. With FETs, the current that flows between the active terminals of the transistor is principally controlled by the voltage across its gate-source terminals. This can be achieved by applying a voltage to the transistor's control terminal (gate). The control terminal generally draws negligible current. With BJTs, the transistor generally needs to be forward-biased at its base-emitter junction for the collector-emitter diode to become conducting. This is typically achieved by applying a voltage to the transistor's control terminal (base). Thereafter, the current flowing between the active terminals (i.e. across the base-emitter function) is a multiple of the current flowing into the control terminal.